Since cable insulation with low thermal conductivity occupies a large proportion of highvoltage cable, an optimization analysis on dynamic thermal behavior of cable insulation can be very useful to improve the accuracy of cable dynamic thermal rating. In this paper, the dynamic thermal analysis of cable insulation is carried out by combining the theoretical method and finite-element analysis (FEA) method. Based on the analysis, it is proved that using IEC recommended transient thermal model of cable insulation will bring certain error to cable dynamic temperature evaluation, especially at the early stage of cable temperature rise. Moreover, in this paper, an implementable optimization method for transient thermal model of cable insulation is developed. The improvement of the optimized model compared with the IEC model on cable dynamic thermal rating is verified by the FEA method. The results confirm that the optimized model can better model the dynamic thermal behavior of cable than the IEC model and the improvement is more obvious for dynamic thermal rating of cable with high voltage level and under large load. The methodology developed in this paper can pave a way for electricity utilities to increase cable utilization while still ensuring cable reliability.INDEX TERMS Dynamic thermal analysis, ampacity, high voltage power cable, transient thermal model, optimization.
With the increase in electricity demand, the ampacity calculation based on the dynamic thermal rating (DTR) technology is increasingly significant for assessing and improving the power transfer capacity of the existing overhead conductors. However, the DTR models now available present some inadequacies in measurement techniques related to wind speed. Therefore, it is essential to propose a new model instead of wind speed measuring in DTR technology. In this paper, the influence analysis of various weather parameters on the conductor ampacity is carried out by using the real weather data. Based on the analysis, it is confirmed that the impact of wind speed is significant, especially in the case of the low wind speed. Moreover, an equivalent heat transfer (EHT) model for DTR technology is proposed instead of wind speed measuring. For this EHT model, the calculation of conductor ampacity is realized through investigating the correlation of heat losses between the heating aluminum (Al) ball and conductor. Finally, combined with the finite element method (FEM), the EHT model proposed in this paper is verified by the Institute of Electrical and Electronic Engineers (IEEE) standard. The results indicate that the error of the EHT model is less than 6% when employing the steady thermal behavior of the Al ball to calculate the ampacity. The EHT model is useful in the real-time thermal rating of overhead conductors. It can increase the utilization of overhead conductors while also avoiding the limitation of the existing measurement techniques related to wind speed.
Ground wire breakage accidents can destroy the stable operation of overhead lines. The excessive temperature increase arising from the contact resistance between the ground wire and armor rod in the contact terminal is one of the main reasons causing the breakage of ground wires. Therefore, it is necessary to calculate the equivalent resistance for ground wires twined with armor rods in contact terminals. According to the actual distribution characteristics of the contact points in the contact terminal, a three-dimensional electromagnetic field simulation model of the contact terminal was established. Based on the model, the current distribution in the contact terminal was obtained. Subsequently, the equivalent resistance of a ground wire twined with the armor rod in the contact terminal was calculated. The effects of the factors influencing the equivalent resistance were also discussed. The corresponding verification experiments were conducted on a real ground wire on a contact terminal. The measurement results of the equivalent resistance for the armor rod segment showed good agreement with the electromagnetic modeling results.
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